Technical Field
The present disclosure is directed to tension members such as those used in elevator systems for suspension and/or driving of the elevator car and/or counterweight.
Description of the Related Art
Traction elevators are widely used. In general, a traction elevator system can include a car, a counterweight, one or more tension members interconnecting the car and counterweight, a traction sheave to move the tension member, and a motor-driven machine to rotate the traction sheave. The sheave is formed from cast iron.
In some elevators, the tension member is a rope formed from twisted steel wires. In other elevators, the tension member is a belt with the twisted wires retained in a polymer jacket. In any event, the transfer of the propulsive load between the sheave and the tension member requires coupling of shear forces along the contact length between the sheave and the tension member. With a belt as the tension member, if the shearing force exceeds the total pullout strength along the contact length, the jacket may crack, deform, or even separate from the belt.
In general, a conventional elevator tension member can include a plurality of steel wires of specific number, size and geometry for purposes of strength, cost of production, and/or durability. The polymer jacket used to retain the steel wires is usually made of polyurethane or other suitable polymer materials. However, as the tensile strength of steel is significantly higher than that of polyurethane, the polymer jacket may be susceptible to premature wear under the aforementioned shear forces, especially along the contact length between the steel wire and the iron sheave.
One way to address this issue is to reinforce the jacket with secondary tension members. For example, one elevator belt is known as including a plurality of planar steel cords encased in a polyurethane jacket, which is reinforced with a plurality of polymer cords distributed throughout the entire jacket. Moreover, each polymer cord is extending through the entire length of the belt. While effective in providing reinforcement to the elevator belt, the polymer cords may increase bending stiffness and may cause localized stress concentration, either of which may adversely affect the performance or service life of the elevator belt. Moreover, the polymer cords distributed throughout the entire jacket may increase the production cost and production time of the elevator belt.
Some power transmission belts, such as timing belts or serpentine belts in automobiles, includes interwoven reinforcement fibers encased in a polymer jacket. Such designs are labor intensive and consume more material, but are necessary for the strength of the belt due to the lack of stronger primary tension members (e.g. steel wires) in the power transmission belts.